The two main leaders of the republican party, which represents the IRA and has played a significant role in the current peace process, have expressed anger and horror at the attack.

The party's president Gerry Adams said: "I am totally
horrified by this action. I condemn it without any equivocation whatsoever."

The wording is significant, since Mr Adams has in the past refused to be so outspoken, even following attacks thought to be also carried out by republican splinter groups since the ceasefire.

After the murder of a retired police officer in March, Sinn Fein called on those opposed to a settlement to stop the killing and throw their weight behind the peace process.

Mr Adams described another shooting in May as a worrying development.

The MP broke off his holiday to return home after hearing of the attack, which is believed to be the work of a dissident terror group opposed to the ceasefire and peace process.

His colleague Martin McGuinness, the chief negotiator for Sinn Fein, was already in Omagh.

He said: "This appalling act was carried out by those opposed to the peace process.

"It is designed to wreck the process and everyone should work to ensure the peace process continues."

Condolences

Mr McGuinness spoke further after spending four hours in the town and said he was appalled, disgusted and angry at the attack.

Martin McGuinness: "We all need to keep our nerve"

He told BBC News 24: "I would like to take this opportunity to express my condolences to all of those families who have lost their loved ones and to all of those people who have been injured."

He said he believed the attack was the work of what he called, "one of the small, unrepresentative republican dissident groupings".

He predicted that some groups may disassociate themselves from the action, and he would be interested to find out who was responsible.

Whoever it was, he said: "I think they have made a very serious mistake."

They had no real support, and they had killed and injured Protestants and Catholics, but mainly people from small nationalist villages.

"All of them were suffering together. I think all them were asking the question 'Why?', because so many of them had great expectations, great hopes for the future."

Releases must continue

Mr McGuinness, who is the party's other MP, pleaded for calm and for the peace process and all ceasefires to be maintained: "I think we all have to keep our nerve at this time.

"We're living through a very important period in Irish history. An awful lot of hopes are running on the peace process.

"People have placed their faith in their political leaders, and I would hope that this terrible action would compel all the political leaders in the north of Ireland to come together and ensure that these people do not win."

That meant prisoners should still be released in accordance with the programme outlined in the Good Friday agreement.

Any move away from the terms of the agreement would represent a victory for the bombers since this is precisely what they wanted.

However some unionist politicians say the release of prisoners and what some see as appeasement of terrorists is encouraging an attitude that such tactics are effective.